This invention relates to internal combustion engines, particularly gas turbine engines associated with aircraft propulsion. More specifically, the invention relates to a method and apparatus for limiting ingestion of ground debris into the inlet of such engines.
Internal combustion engines such as a gas turbine engine generally require large quantities of air flowing at high velocities to produce motive thrust or power generation. It is well known in the art that debris may become entrained in the airflow drawn into the engine inlet. Gas turbine engines mounted on aircraft are particularly susceptible to ingestion of ground debris associated with airfield runways during taxi, takeoff and landing. Some of these engines have exhibited rapid performance deterioration and reduced service life caused by airfoil erosion resulting from the abrasion interaction of the debris with the airfoil sections of the engine. Furthermore, if the debris ingested into the engine is comprised of large stones or other objects, engine failure with catastrophic consequences may result from instantaneous damage to the internal parts of the engine.
It is also well known in the art that, while a portion of a performance deterioration is caused by ingestion of airborne particles into the engine, significant performance deterioration results from ingestion of ground debris into the engine caused by a vortex formed between the engine inlet and the ground. More specifically, as described in the prior art the phenomenon of vortex formation attendant to aircraft gas turbine engines is similar to that occurring in nature and known in its more severe form as a tornado and in its less severe form as a dust-devil. The vortex disposed beneath the inlet of a gas turbine engine is fundamentally similar to those aforementioned vortices found in nature except, however, each is caused by different conditions. In nature, the vortex is formed by the interaction of horizontal surface winds with the vertical upflow of warm air rising to a higher less densified strata. With the gas turbine engine, horizontal surface winds coact with the vertical flow of air beneath the engine to form a swirling vortex extending from the engine inlet downward to the runway surface. As with its nature-induced counterpart, the dust-devil, the vortex associated with the gas turbine engine will, upon contact with the ground, remove debris therefrom scattering the debris upward and forward of the engine inlet such that it is entrained in the airflow stream entering the engine inlet.
Prior attempts to obviate vortex-induced ingestion of foreign particles into the engine inlet have been varied and many. One such attempt has been simply to conduct intensive cleanup of airfield runways. This approach, although simple and straightforward, has proved to be expensive due to the rapid accumulation of runway debris and the high cost of cleaning equipment. Another approach utilized screens disposed in or around the engine inlet to filter the air flowing into the engine. This attempt proved unsatisfactory since the screens tended to clog with debris and retard airflow into the engine under normal flight cruising conditions. Retractible screens did not offer acceptable solution to the problem since retraction dislodged the particles from the screen and ingestion into the engine inlet occurred.
Another prior art approach utilized forward blowing air jets positioned to impinge upon the ground in front of the engine inlet to blow away debris. However, this approach blew debris up off the ground and into the airstreams flowing into the engine inlet. Subsequent techniques also utilized an air jet but in a somewhat different manner. One such approach provided for the discharge of pressurized air from a point aft of the engine inlet and in the forward direction to strike and blow away the vortex origination center. Finally, air jets were disposed ahead of the engine inlet to discharge air in the aft direction to create an artificial headwind which opposes the formation of the vortex. Neither of these approaches has proven to be entirely satisfactory. In particular, a boom housing the air jets and disposed ahead of the engine inlet must be provided with anti-icing equipment so as to preclude the formation of ice thereon under flight cruise conditions. Without such equipment, ice breaking away from the boom may be carried into the engine, causing significant damage. The present invention overcomes the deficiencies associated with these prior techniques by providing a novel and more efficient method and apparatus for preventing ingestion of ground debris into the engine inlet.